Among the currently available hearing aids, ITE type hearing aids are widely used. For example, an ITE type hearing aid may be used for a sole-ear auditory handicapped person, that is a person having one healthy ear and the other ear having hearing impairments. Even in the case of the sole-ear auditory handicapped person, he or she may wear hearing aids onto both ears, that is, the one healthy ear and the other troubled ear. In the sole-ear auditory handicapped person there is no wearing effect of the hearing aid at the healthy ear side, and as such sound signals amplified at the troubled ear side should be transmitted to the healthy ear side via external circuit cables, so as to be heard via the hearing aid worn at the healthy ear side. In this manner, the wearer can hear sounds coming from both the troubled ear side and the healthy ear side.
In the above-described conventional hearing aids for sole-ear auditory handicapped persons, one microphone is incorporated in an ITE type hearing aid cell that is inserted into a troubled ear, and an ear cell including a receiver is inserted into the healthy ear so that signals amplified at the troubled ear side can be heard at the healthy ear side.
The conventional hearing aids problems arise because a time delay is produced in the process of converting the electric signals amplified at the troubled ear side into a sound pressure at the healthy ear side. That is, the conventional hearing aid for a sole-ear auditory handicapped person is employed without considering a time delay between the healthy ear side and the troubled ear side. Thus, a wearer who wears the conventional hearing aid for a sole-ear auditory handicapped person may lose a directional sense with respect to sounds. Further, a hearing ability of the healthy ear may be weakened since an ear cell is inserted into the healthy ear.
Many auditory handicapped persons have one healthy ear and the other troubled ear. Thus, it is necessary to develop a hearing aid for a sole-ear auditory handicapped person. In particular, it is necessary to develop a hearing aid with which sounds coming from both ear sides can be heard well even though the sole-ear auditory handicapped person wears a hearing aid cell and an ear cell in his or her both ears, respectively.